We are a small development staff responsible for extending a vendor supplied application (and database). We make relatively few changes to the schema, and more changes to static data.
Only 2-3 developers modify schema. Some 10 are application developers who may modify static data using the applications interface (as opposed to SSMS).
Is there a suggestion to configure Sql Source Control 2.1 for shared mode to support most application developers, and dedicated mode for 2 or 3 others?
In shared mode, the events that would trigger a commit are:

Application developer request

Before and after applying a vendor supplied update

Periodically

At code freeze

Other question: What is polling about? What does it do? Is it employed in either or both dedicated and shared development model?[/list]

The shared or dedicated model relates to how the developers access SQL Server.

In a dedicated model, each person has a local instance of SQL Server installed in a sandboxed environment.

In a shared model, each developer has SSMS but they each connect to a shared, single instance of SQL Server which hosts the DB.

I guess in your situation, a commit would be triggered automatically when:

1) A developer made a change to the schema in either the sandboxed or shared model
2) If a vendor update applied over your shared or dedicated DB's, you would then be prompted to commit that version
3) When you wanted to add static data, or if static data had been amended either locally or one of the developers dedicated instances

On the subject of polling, this is something that we do within the DB itself to check for changes to objects and to generate the blue blobs by objects that have been modified. It's used in both models.
HTH!